1. Technical Field
The present disclosure generally relates to electronic devices and in particular to wireless charging of portable electronic devices.
2. Description of the Related Art
With an ever increasing demand for smart portable devices to be used for various applications, there is an accompanying increase in the development of low-power portable/mobile devices, including wearable devices such as smart watches and fitness bands. These devices are typically smaller devices which utilize smaller connectors such as a micro-USB type connector to charge the device. However, the micro-USB type connector is too large for charging some of the smaller devices. Wireless charging is a solution to the large connector problem. The Wireless Power Consortium (WPC) has established the Qi standard (i.e., inductive power standard) which can be used in lower power device applications. Wireless charging involves utilizing transmitter and receiver coils to provide a power transfer.
In wireless charging systems, there is an inherent power dissipation tradeoff between the large inductance needed for signal detection and a lower inductance that is optimal for power transfer in Qi compliant wireless power receivers. Current solutions require a designer to pick a receiver inductance that is a balance between detection range and power transfer efficiency. If the trade off of detection range for a wider power transfer operating range is too great, a situation can be presented in which a user can start charging and not be able to restart the device. This leads to a poor charge experience where the device charges completely (i.e., 100% charge) but then the charger shuts off and the device becomes discharged.
Additionally with the introduction of the new medium power Qi 1.2 standard, picking an optimal inductance value will be even more difficult as the low power standard specifies 5 Watts (W) delivered, while the new medium power goes to 15 W.